Antagonistic potential and biological control mechanisms of Pseudomonas strains against banded leaf and sheath blight disease of maize

Abstract

Abstract There is increased interest in developing biological control agents to effectively combat the banded leaf and sheath blight (BL&SB) caused by Rhizoctonia solani, a devastating disease that affects maize and many other crops worldwide. In the current study, we screened 22 rhizobacteria(AS1-AS22) recovered from grassland in the Pithoragarh region of the Central Himalayas for antagonism against Rhizoctonia solanif. sp.sasakii. Two Pseudomonas strains, AS19 and AS21, exhibited the highest in vitro inhibition of fungal mycelium, with cell cultures of AS19 and AS21 showing inhibition was 57.04% and 54.07%, respectively, and with cell-free culture filtrate showing67.41%and 65.74%, respectively. The two bacteria also prevented sclerotium growth. The strains AS19 and AS21were identified as Pseudomonas sp. by 16S rDNA phylogeny and deposited under accession numbers NAIMCC-B-02303 and NAIMCC-B-02304, respectively. The biocontrol mechanisms in the selected strains were investigated in a plate assay and a pot trial. The scanning electron micrograph of the dual culture plate assay showed the intense degradation of fungal mycelium by strains AS19 and AS21. Both strains also produced hydrolytic enzymes. There was a significant reduction in BL&SB disease incidence (DI) with the application of strains AS19 and AS21 in a pot trial using maize crops. The decrease in DI ranged between 25–38.33% in the treatments receiving foliar sprays of two antagonistic isolates 48 h before pathogen inoculation. The results showed that the two Pseudomonas strains act through induced systemic resistance (ISR) and are potent BCAs. The two strains, AS19 and AS21, exhibited broad-spectrum in vitro antifungal activity against Alternaria triticina, Bipolaris sorokiniana, Rhizoctonia maydis, and Fusarium oxysporumf. sp.lentis. Before the commercial-level exploitation of these two BCAs, further studies must be done to validate their biocontrol activity in field trials and to identify a bacterial metabolite responsible for inducing systemic resistance.